The present invention relates to a novel upper reflector system for a fluorescent troffer.
Work spaces are typically illuminated by the standard two foot by four foot (2.times.4) fluorescent troffer containing three forty watt fluorescent lamps. The parabolic louver, such as that found in the P-2 fluorescent fixture manufactured by Columbia Lighting, Spokane, Wash., represents such standard 2.times.4 fluorescent troffer. This standard unit possesses a parabolic louver which exhibits relatively high efficiency, low glare, and good spacing ratios perpendicular to the axis of the lamps. However, the oblong shape of the 2.times.4 troffer creates an orientation pattern on the ceiling which may not be compatible with the design and use of interior space being illuminated.
For purposes of aesthetic design and for greater ease of installation a square two foot by two foot (2.times.2) troffer would be preferred. Troffers of this dimension have been produced using two 40 watt u-shaped lamps or four two foot long 20 w lamps. Unfortunately such 2.times.2 troffers supply less than two-thirds of the light of the three lamp 2.times.4 troffers and must be spaced closer together to produce the same light levels. A more efficient "twin tube" 40 w fluorescent lamp, small enough to fit in a 2.times.2 troffer, has been developed. However, troffers using these lamps would still be unable to serve as a direct replacement for 2.times.4 troffers because of the poor distribution of light parallel to the lamp axis, i.e. outwardly from the ends of the lamp. While this poorer distribution of light in the parallel direction also occurs in standard 2.times.4 troffers, the four foot tube length in the parallel direction reduces the end-to-end gap between troffers and, thus, more light is provided on the working surface halfway between units. Since a 2.times.2 troffer does not have this compensating extra tube length, these units must be spaced more closely together in the parallel direction, resulting in the use of more troffers for a given area.
For design purposes the term "spacing ratio" may be defined as the horizontal spacing between adjacent troffers divided by the mounting height of the troffers above the working surface. The spacing ratio is used to indicate the maximum spacing which will provide uniform illumination on the surface. Existing 2'.times.2' troffers generally exhibit spacing ratios of about 1.5 in a plane normal or perpendicular to the lamp axis, but only about 1.2 in a plane parallel to or along the axis of the lamp and intersecting the space to be lighted. For a typical 9' ceiling and a 30" desk height (61/2' mounting height) such 2.times.2 troffers can therefore be spaced approximately 10' apart perpendicular to the lamp axis, but only 8' apart with the lamps oriented end-to-end. Complex electronic devices in the work place exaccerbate the lighting problem since the floors of such work places are often raised six inches to accommodate cables and wires. Thus, a higher spacing ratio is required in such an area since the floor to ceiling height is decreased.
In addition, glare or brightness from fluorescent troffers at angles of 60.degree. through 90.degree. from nadir must be controlled in all directions. For example, video display terminals are very susceptible to glare or brightness causing obscuration of characters appearing on the screen. The mere adding of additional shielding in a troffer to block this brightness reduces the overall efficiency of the unit. With a 2.times.2 troffer producing the same amount of total light as a 2.times.4 troffer, the brightness averaged across the projected area of the troffer (average foot lamberts) could be expected to be twice as great in a 2.times.2 troffers in a 2.times.4 troffer at these higher, glare angles.
U.S. Pat. Nos. 4,065,667, 4,575,788 and 4,651,260 describe reflector systems for high intensity discharge lamps generally employed in outdoor environments. Such luminaires in the prior art are generally not adaptable to fluorescent indoor lighting systems. U.S. Pat. No. 4,562,517 shows an upper reflector system for a fluorescent lighting unit which generally controls distribution of light in the perpendicular or normal plane for use with u-shaped fluorescent tubes and circular fluorescent tubes.
A compact 2.times.2 troffer which solves the light distribution and glare control problems encountered in the prior art would be a great advance in the lighting field.